The present invention is related to the medical treatment of the myocardium and more specifically to devices for accessing the myocardium and to techniques for magnetically guided myocardial interventions.
Various diseases exist that require precise access to the heart muscle. Current treatment modalities have been limited by the ability to direct and hold treatment devices in the proper location in a beating heart. Consequently, major open surgical interventions are common where a minimally invasive approach would be preferable. One such procedure is myocardial revascualrization and the inventions are described in that context.
For example patients who exhibit ischemic heart disease and who experience angina can be treated by perforating the wall of the ventricle. It is not entirely understood why this form of injury improves the cardiac performance of the patient. Some evidence suggests that the healing response to the injury causes new blood vessels to form and increases the size of existing blood vessels. The additional blood flow relives the symptom angina.
The first myocardial revascularization experiments were performed with a laser, which was used to perforate the heart from the xe2x80x9coutsidexe2x80x9d of the heart. In general the laser energy was applied to the exterior wall of the ventricle and activated. In use the laser energy burns and chars a hole in the heart wall. The blood pool inside the heart prevents further injury to structures within the heart.
More recently it has been proposed to revascularize the heart wall though a percutaneous transluminal approach. See for example Nita U.S. Pat. No. 5,827,203. This technique can be used to place a catheter against the endocardial surface of the heart. However the heart wall is in constant motion and this relative motion renders creation of the lesion problematic.
In general, both improved devices and techniques are needed to advance this therapy.
The methods and devices of the invention are useful in a variety of settings. For purposes of illustration the invention is described in the context of myocardial revascularization which is one instance where the catheter is magnetically navigated to a site near a wall of the heart. Other examples of treatments include the repair of septal defects and heart biopsy. It is anticipated that some forms of cardiomyopathy may respond to therapies delivered with these tools as well. For this reason it must be understood that the devices and methods can be used in a variety of contexts within the body.
A magnetically navigable and controllable catheter device is deployed at the heart wall and this device tunnels into the myocardium. Any of a variety of canalization technologies can be used to tunnel into the heart wall causing mechanical disruption of the tissues, including mechanical needles and RF energy sources as well as direct laser and heated tips. The catheter device is guided by externally applied magnetic fields that are created by a magnetic surgery system (MSS). The MSS applies magnetic fields and gradients from outside the body to manipulate and direct medical devices within the body. The catheter devices of the present invention include magnetic elements that respond to the MSS field or gradient. In general the physician interacts with a workstation that is associated with the MSS. The physician may define paths and monitor the progress of a procedure. Fully automatic and fully manual methods are operable with the invention.
Although several energy sources are disclosed that can be delivered by the catheter trough its distal tip, an RF heated tip is preferred since it can be used both to cut and to coagulate tissues depending on the delivered energy level. This feature is shared with laser-heated tips and other thermal catheter technologies but RF devices have a greater history of use for coagulation.
The proposed methods of the invention can be used to move the catheter device both along and across muscle planes within the heart tissue so that a complex wound pathway or xe2x80x9ctunnelxe2x80x9d can be created. This structured shape can be used to retain xe2x80x9cimplantxe2x80x9d materials such as growth factor. Growth factor or other drugs may be embedded in or on absorbable material. In some instances it may be desirable to combine the drug with a magnetic particle so that the gradient and fields can be used to position and retain the drug in the tissue. For example the lesion can be in the form of a xe2x80x9cblindxe2x80x9d hole and the drug can be left behind in the wound and retained magnetically inside the tissues.
For purposes of this discussion the term xe2x80x9cablationxe2x80x9d or xe2x80x9clesionxe2x80x9d should be considered to include thermally damaged tissues eroded and charred tissue and other processes that destroy or remove tissue. Typical devices to carry out this xe2x80x9cinjuryxe2x80x9d include mechanical RF electrical Thermal optical and ultrasonic means. Throughout the description the wound is referred to as a tunnel in recognition of its shape.